It has long been recognized that, in a radiotelephone system with at least one movable station in a communicating pair of stations, it is advantageous to provide for adjustment of transmission power of transmitting stations from time to time. The stations will then use only the lowest reliable power level and thereby reduce the likelihood of interference among cochannel stations engaged in different calls. One example of such a system is contained in U.S. Pat. No. 3,732,496 to M. L. Boyer. Another example, controlling movable station power in a cellular radio system, is U.S. Pat. No. 3,906,166 to M. Cooper et al. In the U.S. Pat. No. 2,678,998 to W. R. Young, Jr., an element of hysteresis is employed in the adjustment algorithm to avoid excessive switching when a subscriber unit is near the edge of a zone. A recent paper by T. Nagatsu et al., "Transmitter Power Control for Cellular Land Mobile Radio," IEEE Global Telecommunications Conference, Nov. 11-Dec. 1, 1983, pages 1430-1434, shows consideration of systems in which each of a pair of communicating stations directs adjustments at the other.
A J. Kojima U.S. Pat. No. 4,435,840 teaches a radio system in which station output power is adjusted in response to changes in traffic level to modify service area coverage.
Dynamic power control systems of the type just outlined typically engage in an iterative measuring-signaling-step-adjusting cycle until a desired transmission power level has been achieved. If each station of a communicating pair is aiding the other, each must include the same equipment both to control its own power and to help other stations adjust their transmission powers.
After such changes in transmitted power in systems where call handoff is based on some function of signal power, there are corresponding changes in the distance from the cell antenna site at which a subscriber unit call handoff will take place. Such distance changes create an uneven call handling situation in that, during low power operation, a subscriber unit call may be terminated because its signal quality is too low and yet the unit is too far from another cell site to improve its situation. Likewise, during high power operation, the unit may operate beyond its proper cell site coverage area into an adjacent cell coverage area and from there cause undue cochannel interference. This is especially true of personal portables which may experience wide swings in coverage as they are moved about among the floors of a tall building or even from one plane to another on the same floor.